Rotary tuner for circular electric mode crossed field tube

ABSTRACT

A coaxial magnetron of the type including a circular electric mode cavity coupled to a vane resonator system is tuned by means of a tuning structure movable in the circular electric mode cavity. The tuning structure includes an array of electrically conductive reactive loading elements, such as vanes, reactively loading the resonator and an adjacent array of field perturbing elements. Relative motion is effected between the two arrays of elements to effect a cyclical variation or modulation of the reactive loading on the cavity and thus the output frequency of the tube.

United States Patent Gerard Oct. 21, 1975 [54] ROTARY TUNER FOR CIRCULAR 3,471,744 10/1969 Pryor 315/3977 ELECTRIC MODE CROSSED FIELD TUBE 3,590,312 6/1971 Blank et a1 3,731,137 5/1973 Foreman 315/3961 Primary ExaminerSaxfield Chatmon, Jr. Attorney, Agent, 0r'Firm-Stan1ey Z. Cole; D. R. Pressman; Harry E. Aine {57] ABSTRACT A coaxial magnetron of the type including a circular electric mode cavity coupled to a vane resonator system is tuned by means of a tuning structure movable in the circular electric mode cavity. The tuning structure includes an array of electrically conductive reactive loading elements, such as vanes, reactively loading the resonator and an adjacent array of field perturbing elements. Relative motion is effected between the two arrays of elements to effect a cyclical variation or modulation of the reactive loading on the cavity and thus the output frequency of the tube.

7 Claims, 7 Drawing Figures [75] Inventor: William A. Gerard, Andover, Mass.

[73] Assignee: Varian Associates, Palo Alto, Calif.

[22] Filed: Apr. 18, 1974 21] App]. No.: 461,835

[52] U.S. C1. 315/3961; 315/3959; 315/3977 [51] Int. C1. 1101.1 25/50 [58] Field of Search 315/3951, 39.59, 39.61,

[56] References Cited UNITED STATES PATENTS 2,449,794 9/1948 Steele, Jr. 315/3961 3,333,148 7/1967 Buck 315/3959 3,412,285 11/1968 Gerard 315/3977 X 3,435,284 3/1969 Downing et a1 315/3977 X 3,441,796 4/1969 Cooper 315/3961 US. Patent Oct. 21, 1975 3,914,644

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ROTARY TUNER FOR CIRCULAR ELECTRIC MODECROSSED FIELD TUBE RELATED CASES BACKGROUND or THE INVENTION The present invention relates in general to frequency agile microwave tubes and more particularly to an improved rotary tuner for coaxial magnetrons.

DESCRIPTION OF THE PRIOR ART Heretofore, it has been proposedto tune a coaxial magnetron by rotation of a cylindrical dielectric castellated tuning member in the circular electric mode cavity relative to a fixed or stator similarly castellated dielectric member, whereby the frequency of the magnetron is modulated due to modifying'the electric field within the cavity resonator. Such a tuner is described in U.S. Pat. No. 3,412,285 issued Nov. 19, 1968.

The problem with this prior arrangement is that the castellated cylindrical dielectric tuning structures were centrally disposed in the toroidal shaped coaxial circular electric mode cavity in the high field region thereof. With a substantial amount of dielectric material disposed permanently in the high field region of the circular electric mode cavity the dielectric material substantially resistively loads the cavity, thereby reducing its loaded Q'to an unacceptably low value. In addition, the dielectric members serve to concentrate the electric field in the dielectric material such that when the rotating castellated rotor member is rotated out of registration withthe castellated stator inember,'arcing may tend to occur through the gap established between the two members. For these and other reasons the aforedescribed tuner has not proven satisfactory in practice.

It is also known from the prior art, relating to vane magnetrons of non-coaxial type, to tune the tube by rotating an apertured metallic cylinder adjacent the back walls of the individual vane resonators. The rotating metallic cylinder was apertured with an array of apertures there being one aperture for each of the respective vane resonators. As the apertured metallic tuning member is rotated, the tuning member presents to the rear wall of the respective vane resonators a solid wall portion followed in succession by an aperture thus effectively varying the position of the back wall of the vane resonator and effecting tuning of the resonator system. While such a tuner results in a cyclical modulation of the output frequency of the tube, this tuner arrangement has certain disadvantages which include instabilities in the output frequency, inability to obtain a tracking output signal for tuning a local oscillator or a receiver, due to such frequency irregularities, and the difficulty of fabricating the tuning structure due to its relatively small size and requirement that it operate within the vacuum envelope of the tube.

Still others have proposed schemes for tuning a coaxial magnetron wherein a circular array of rotatable ceramic paddles were Iocatedwithin the circular electric mode cavity. The'paddles were driven in synchronism by a planetary gear arrangement. As each of the pad.- dles turned into a position of alignment with the electric field of the circular electric mode, the tube was tuned to its lowest frequency and conversely when the paddles were turned at right angles to the electric field vector the tube was tuned to its highest frequency.

A significant disadvantage of the rotating dielectric paddles is the relatively large number of rotating parts,

gears, and bearings that are required.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved rotary tuner for coaxial magnetrons.

In one feature of the present invention, a cavity resonator as coupled to a microwave interaction structure for stabilizing the operating frequency thereof is tuned by effecting relative movementbetween a plurality of electrically conductive reactive loading elements coupled to the cavity for reactively loading same and an adjacent plurality of electromagnetic field perturbing elements, whereby the resonant frequency of the cavity resonator and thus the output frequency of the tube is modulated.

In another feature of the present invention, the cavity being tuned is a circular electric mode cavity of a magnetron which is coupled to the microwave interaction circuit comprising a vane resonator system.

In another feature of the present invention, the electrically conductive reactive loading elements are disposed along one of the walls of the cavity resonator being tuned.

. In another feature of the present invention, the tuning structure includes a first array of electrically conductive reactive loading elements coupled to the fields of the resonator and a second array of dielectric field perturbing elements disposed adjacentv the array of loading elements for cyclically varying the reactive loading effect of the array of electrically conductive loading elements on the cavity being tuned in response to relative movement between the arrays of first and second tuning elements.

"Other features and advantages of the present invention will become apparent upon a perusal 'of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of a coaxial magnetron incorporating features of the present invention,

' FIG. 2 is an enlarged view of a portion of the structure of FIG. 1 delineated by line 2-2,

FIG. 3 is a sectional view of the structure of FIG. 2

taken along the line 3-3 in the direction of the arrows and showing the dielectric tuning member in a first position, I

FIG. 4 is a view similar to that of FIG. 3 depicting the dielectric tuning structure in a second position,

FIG. 5 is a sectional view of the structure of FIG. 2

taken along line 5-5 in the direction of the arrows,

FIG. 6 is a fragmentary detail view of a portion of a structure similar to FIG. 2 and depicting an alternative embodiment of the present invention, and

FIG. 7 is a sectional view of the structure of FIG. 6 taken along line 7-7 in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS for emitting a stream of electrons in an annular interaction region defined between the cathode and surrounding cylindrical anode 13 including a circular array of anode vanes 14 projecting inwardly from the cylindrical anode 13 toward the centrally disposed cathode 12 for defining a microwave intereaction circuit. A circular array of elongated slots 15 is provided in the cylindrical wall of the anode 13 for providing wave energy communication with alternate vane resonators defined by the region between adjacent vanes 14.

A toroidal shaped cavity resonator 16 is disposed surrounding the anode 13 in electromagnetic field exchanging relation with the vane resonators via the intermediary of the coupling slots 15. Since only alter nate vane resonators are directly coupled to the toroidal cavity 16, the 11' mode of oscillation of the vane resonator system excites the TE circular electric mode of the toroidal resonator 16. A cylindrical wave permeable vacuum envelope 17 is disposed surrounding the cylindrical anode 13 such that the electron interaction region between the cathode 12 and the anode resonators 14 may be evacuated by evacuation of the envelope 17 while allowing the external resonator 16 to operate at atmospheric pressure or to be pressurized with a suitable electrically insulative gas, such as SF A pair of cylindrical permanent magnet structures 18 are disposed within the anode 13 in coaxially spaced relation from the cathode and on opposite sides of the interaction gap between the cathode 12 and the surrounding vane resonators 14. The permanent magnets 18 are polarized to produce an axially directed magnetic field through the annular interaction region defined between the tips of the vane resonators l4 and the cathode emitter 12.

The toroidal cavity resonator 16 is defined by the region of space bounded by the outside of the cylindrical anode wall 13 and the inside of a cylindrical coaxially disposed radially spaced wall 19. The top and bottom end walls of the resonator 16 are defined by annular electrically conductive plates 21 and 22 joined to the outer side wall 19 and to the vacuum envelope 17.

Referring now to FIGS. 1-5, there is shown a tuning structure 23 for effecting frequency modulation of the output frequency of the tube. More specifically, an array of radially directed electrically conductive lands or vanes 24 are formed in the inside surface of the upper wall 21 of the resonator 16 to define an array of reactive loading elements coupled to the electromagnetic fields of the excited TE mode of the resonator 16 for reactively loading the resonator 16. A second rotary tuning member 25 is formed by an annular dielectric plate 26, as of low loss ceramic such as alumina, beryllia, sapphire, etc. The annular dielectric plate 26 includes an array of apertures 27 with the web portion of the plate which remains between adjacent apertures 27 defining a circular array of field perturbing elements 28.

In a preferred embodiment, the circumferential extent of the apertures 27 is the same as the circumferential extent of the space (groove) between adjacent vanes 24 such that when the angular position of the rotatable tuning member 25 is in the position as shown in FIG. 3 the inductive reactive loading effect of the reactive loading elements 24 is a minimum and therefore the output frequency of the tube is at its highest frequency. However, when the rotatable field perturbing member 26 is rotated to the position such that the perturbing elements 28 are in registration with the spaces (grooves) between adjacent reactive loading elements 24, the reactive loading effect of the elements 24 is a maximum on the operating frequency of the cavity 16 such that this relative position corresponds to the lowest frequency of the cavity.

A circular array of axially directed dielectric tab portions 29 of the dielectric tuning member 25 are fixed, as by brazing, to the lower end of a cylindrical conductive actuator 31 which passes through an annular slot in the upper wall 21 of the resonator 16. The cylindrical actuator 31 is afiixed to an axle 32 (see FIG. 1) which is rotatably supported from a cup-shaped housing 33 via the intermediary of bearing assembly 34. A

motor 35 is affixed to the axle 32 for rotatably driving reached operating speed. This time varying signal is employed for tuning the receiver of aradar or the like to the operating frequency of the tube 11 for improved signal-to-noise ratio.

Output microwave energy is extracted from the coaxial resonator 16 via a conventional output coupling iris 37 and waveguide 38 for propagation to a suitable load such as an antenna, not shown. If there are N number of vanes 24 and N number of field perturbing members 28, the output frequency of the tube will be swept across its tunable band 2N times per revolution of the rotary tuning member 25. Thus, the generator 36 preferably has the same number of poles as there are reactive loading elements 24.

Referring now to FIGS. 6 and 7, there is shown an alternative embodiment of the present invention. This embodiment is similar to that of FIGS. l-5 with the exception that the rotating tuning member 25 comprises a slotted dielectric cylinder 26 provided with anarray of apertures 27 (slots), the apertures corresponding to the grooves or spaces defined between longitudinally directed lands or vanes 24' provided in the inside surface of the outer side wall 19 of the cavity 16. The circular array of longitudinally directed vanes 24' serves as an array of reactive loading elements for inductively reactively loading the cavity 16.

The web portion 28, defined between the adjacent apertures 27', of the cylindrical dielectric member 26' serves as an array of field perturbing elements, in the manner as previously described with regard to FIGS. 3 and 4, for modulating the reactive loading of the cavity 16 in accordance with the relative position of the field perturbing portions 28 relative to the lands or vanes 24. The cylindrical tuning member 25' is affixed to the metallic cylindrical actuator 31 which in-tum is rotated via the axle 32, in the manner as described with regard to FIG. 1.

Thus, it has been shown that the reactive loading members may be disposed along the top wall 21 or along the side wall 19 or, if desired, may be disposed along the bottom wall 22. Furthermore, such reactive loading members 24 and 24 may be located along both the top and bottom walls 21 and 22 as well as along the side wall 19 for effecting greater tuning range.

As thus far described, the rotary tuner 25 is utilized in a coaxial magnetron of the type wherein the stabilizing cavity 16 surrounds the array of coupled vane resonators 14. While this is a preferred embodiment, an alternative embodiment is of the type wherein the vane resonator system 14 surrounds a central circular electric mode resonator. A tube of this latter type is disclosed and claimed in U.S. Pat. No. 3,231,781 issued Jan. 25, 1966 and assigned to the same assignee as the present invention. In such a tube, the top wall of the central resonator could include the array of radially directed vanes 24 and the rotatable dielectric plate 25 would include an array of radially directed apertures to define the array of perturbing members 28.

A tube incorporating the tuner of the present invention provides means for rapidly dithering or sweeping the output frequency of the tube to and fro over a certain band of frequencies. An advantage to the tuner of the present invention is that the dielectric tuning structure 25 is not located in a region of intense electric field and furthermore the amount of dielectric is substantially less than that previously proposed in the aforecited U.S. Pat. No. 3,412,285, because the field is concentrated by the conductive loading elements whereby the loaded Q of the cavity is not reduced below a useable value. Furthermore, the tuner of the present invention employs a much larger number of teeth in the relatively rotatable tuning structures such that the rate at which the rotating tuning member must be turned to achieve a certain modulation frequency is substantially reduced compared with the tuner proposed in the aforecited U.S. Pat. No. 3,412,285. Reducing the speed of the tuner increases bearing life and thus operating life of the tube or, if operated at the same speed, produces a much higher rate of frequency modulation of the output frequency of the tube.

What is claimed is:

1. In a microwave tube;

means for generating a stream of electrons;

microwave circuit means in energy exchanging relation with said stream of electrons for generating electromagnetic energy; cavity resonator means coupled to said circuit means for exciting in said cavity a resonance mode affecting the frequency of said electromagnetic energy;

tuner means within said cavity for cyclically varying the resonant frequency of said mode of said cavity, said tuner means comprising a conductive reactive loading structure, a field perturbing structure, and an axis;

said conductive reactive loading structure comprising an array of vanes disposed on a circle about said axis and aligned along radii of said circle such that electric fields of said mode excite electric fields between adjacent vanes whereby said resonance mode is reactively loaded by said vanes;

said field perturbing structure comprising an array of dielectric elements disposed on a circle about said axis and further disposed to intercept fringing portions of said electric fields between adjacent vanes and,

means for producing relative rotation of said reactive loading structure and said field perturbing structure about said axis to cyclically vary the amount of said fringing field intercepted by said dielectric elements, whereby the resonant frequency of said cavity mode and the frequency of said microwave energy are cyclically varied.

2. The apparatus of claim 1 wherein said cavity resonator means includes a chamber which is generally a figure of revolution about a cavity axis.

3. The apparatus of claim 2 wherein said chamber is toroidal shaped having a pair of axially spaced coaxially disposed annular conductive end walls and a pair of radially spaced coaxially disposed axially coextensive cylindrical side walls, and wherein said array of vanes is disposed along at least one of said end walls and side walls of said cavity resonator means.

4. The apparatus of claim 2 wherein said chamber is generally cylindrical and has a pair of axially spaced end walls and a cylindrical side wall and wherein said array of vanes is disposed along at least one of said end and side walls.

5. The apparatus of claim 2 wherein said cavity axis coincides with said axis of said tuner.

6. The apparatus of claim 5 wherein said resonance mode has an electric field which is generally circular about said axis of said tuner.

7. A coaxial magnetron comprising a cylindrical cathode, a cylindrical anode surrounding said cathode and coaxial therewith, an array of anode vanes extending radially inward from said anode wall and defining a plurality of anode resonators, an outer coaxial cavity resonator surrounding said anode wall, coupling slots provided in said anode for coupling energy from said anode resonator to said outer coaxial cavity resonator, tuning means provided within said outer coaxial cavity resonator, said tuning means comprising a first tuning member and a second tuning member, and means for providing relative rotational motion of said first and second tuning members to modify the electric field within said cavity resonator and thereby vary the frequency of said coaxial magnetron, and wherein said first of said tuning members comprises an electrically conductive structure having a plurality of electrically conductive vanes disposed on a circle and aligned with radii of said circle for reactively loading said coaxial cavity resonator, and wherein said second tuning member includes a plurality of dielectric field perturbing elements coupled with the fields of said coaxial cavity resonator for modifying the reactive loading effect of said vanes on said cavity as a function of the relative rotational motion of said first and second tuning members. 

1. In a microwave tube; means for generating a stream of electrons; microwave circuit means in energy exchanging relation with said stream of electrons for generating electromagnetic energy; cavity resonator means coupled to said circuit means for exciting in said cavity a resonance mode affecting the frequency of said electromagnetic energy; tuner means within said cavity for cyclically varying the resonant frequency of said mode of said cavity, said tuner means comprising a conductive reactive loading structure, a field perturbing structure, and an axis; said conductive reactive loading structure comprising an array of vanes disposed on a circle about said axis and aligned along radii of said circle such that electric fields of said mode excite electric fields between adjacent vanes whereby said resonance mode is reactively loaded by said vanes; said field perturbing structure comprising an array of dielectric elements disposed on a circle about said axis and further disposed to intercept fringing portions of said electric fields between adjacent vanes and, means for producing relative rotation of said reactive loading structure and said field perturbing structure about said axis to cyclically vary the amount of said fringing field intercepted by said dielectric elements, whereby the resonant frequency of said cavity mode and the frequency of said microwave energy are cyclically varied.
 2. The apparatus of claim 1 wherein said cavity resonator means includes a chamber which is generally a figure of revolution about a cavity axis.
 3. The apparatus of claim 2 wherein said chamber is toroidal shaped having a pair of axially spaced coaxially disposed annular conductive end walls and a pair of radially spaced coaxially disposed axially coextensive cylindrical side walls, and wherein said array of vanes is disposed along at least one of said end walls and side walls of said cavity resonator means.
 4. The apparatus of claim 2 wherein said chamber is generally cylindrical and has a pair of axially spaced end walls and a cylindrical side wall and wherein said array of vanes is disposed along at least one of said end and side walls.
 5. The apparatus of claim 2 wherein said cavity axis coincides with said axis of said tuner.
 6. The apparatus of claim 5 wherein said resonance mode has an electric field which is generally circular about said axis of said tuner.
 7. A coaxial magnetron comprising a cylindrical cathode, a cylindrical anode surrounding said cathode and coaxial therewith, an array of anode vanes extending radially inward from said anode wall and defining a plurality of anode resonators, an outer coaxial cavity resonator surrounding said anode wall, coupling slots provided in said anode for coupling energy from said anode resonator to said outer coaxial cavity resonator, tuning means provided within said outer coaxial cavity resonator, said tuning means comprising a first tuning member and a second tuning member, and means for providing relative rotational motion of said first and second tuning members to modify the electric field within said cavity resonator and thereby vary the frequency of said coaxial maGnetron, and wherein said first of said tuning members comprises an electrically conductive structure having a plurality of electrically conductive vanes disposed on a circle and aligned with radii of said circle for reactively loading said coaxial cavity resonator, and wherein said second tuning member includes a plurality of dielectric field perturbing elements coupled with the fields of said coaxial cavity resonator for modifying the reactive loading effect of said vanes on said cavity as a function of the relative rotational motion of said first and second tuning members. 